1. Field of the Invention
The present invention relates to a capsule endoscope having a light emitting device and a photographing optical system therein.
2. Description of the Related Art
Conventionally, a capsule endoscope is used in medical and industrial fields. When it is used in the medical field, the capsule endoscope is swallowed so as to enter the body of a patient, and it photographs images inside the body. The photographed images are transmitted as signal out of the body by radio, so that a doctor can observe the inside of the body. The capsule endoscope doesn't have an insertion member like a conventional endoscope, and this means pain is eliminated for the patient.
Generally, the capsule endoscope comprises a cylindrical cover and two dome-shaped covers which cover both ends of the cylindrical cover. One of the dome-shaped covers is a transparent cover, and a light emitting device and a photographing optical system are disposed opposite to the transparent cover. The light emitting device emits light to illuminate an area inside the body through a transparent cover, and the photographing optical system captures an image of the illuminated area inside the body.
In this case, most of the light emitted by the light emitting device permeates through the transparent cover and is radiated inside the body. However, part of the light is reflected by the transparent cover, and the reflected light is input to the photographing optical system. Due to this, flares appear in the photographed image, which deteriorate the quality of the image. Therefore, it is known that the position of the entrance pupil of the photograph optical lens system should coincide with the center of curvature of the transparent cover to prevent the reflected light from entering to the photographing optical system, as shown in Japanese Unexamined Patent Publication (KOKAI) NO. 2003-260025.
However, even if the position of the entrance pupil is located as described above, it is difficult to prevent all the reflected light from entering the photographing optical system.
Further, conventionally, an inorganic LED (light-emitting diode) is used as the light emitting device. However, the illumination range of an inorganic LED is not so large, so several inorganic LEDs have to be provided in the capsule endoscope to obtain a sufficient illumination range. In this case, the inorganic LEDs are arranged around the imaging device, so that other components can not be arranged around the imaging device and it is difficult to miniaturize the capsule endoscope.